This invention relates to an excavating tool having hard facing elements supported in a material-engaging surface thereof and, more particularly, to tools such as excavating teeth, excavating blades, or cutting edges such as those employed on underground mining plows.
Since about the turn of the century workers in the excavating art have employed replaceable earth engaging elements such as two-piece teeth, i.e., the wedge shaped projections on the penetrating edge of a scraper, dipper, bucket, etc. This has also been true of blades and cutting edges and has permitted renewal of the penetrating portion (after the same had become worn) with a minimum of throw-away metal. In some cases in especially abrasive digging, it is not unusual for the tool to be replaced every eight hours.
The need for point replacement (because of wear) was disadvantageous not only because of the cost of the element itself but because of the loss of use of an expensive machine, i.e., down time. Efforts have been made throughout the years to minimize down time by providing temporary locks which were effective to keep the point or other tool in place during operation but which could be readily deactivated to permit quick replacement. Nonetheless, some time was still required for the disassembly of the tool and replacement of the principal material engaging part.
This led the art workers to consider "hard-facing" the excavating teeth, blades, etc. The usual material considered for this purpose was tungsten carbide which had been used for facing machine tools and drill bits. An early attempt in the excavating tooth field is seen in the 1936 patent of Stoody U.S. Pat. No. 2,033,594. There particles of tungsten carbide were placed within the apex groove of the tooth.
A more recent attempt in this field is represented by Jackson et al U.S. Pat. No. 3,790,353 which made use of a wear pad of 70-85% of particles of cemented tungsten carbide and wherein the pad was attached to the upper forward surface of the tooth point. In Engel, et al U.S. Pat. No. 3,805,423, a large insert of tungsten carbide was placed in a recess in the point upper surface. In Baum, U.S. Pat. No. 4,024,902, sintered tungsten carbide particles were dispersed within the steel alloy making up the tooth point. None of these expedients have proved successful. Tooth points equipped with hard facing elements have not worked out primarily because the elements have been gouged or flaked out because of the substantial impacts which occur during excavating.
We have discovered that the life of an excavating tool (such as an excavating tooth point or blade) can be materially increased if the hard-facing elements (generically referred to as "carbides") are supported at an angle to the material engaging surface in which they are positioned, the angle being generally perpendicular to the average force line of the material being engaged by the tool. This results in substantial avoidance of gouging, flaking, cracking, etc. with the result that the life of the tool now approaches that of the hard-facing elements rather than the much shorter life of the supporting alloy steel. Other details, advantages and objects of the invention may be seen as this specification proceeds.